title: Higher body mass index is associated with higher fractional creatinine excretion in healthy subjects.
abstract: BACKGROUND
  Accurate glomerular filtration rate (GFR) measurement in normal to high range is important for epidemiological studies and workup for kidney donation. Creatinine-based equations perform poorly in this GFR range. Creatinine clearance (CrCl) provides a substitute, provided urine is collected accurately and tubular creatinine handling can be accounted for. The latter is poorly characterized in the normal GFR range.
  
  
  METHODS
  Therefore, we studied performance of CrCl, fractional creatinine excretion (FE(creat)) and its determinants in 226 potential kidney donors (47% males, mean 53 ± 10 years). GFR was assessed as (125)I-iothalamate clearance, simultaneously with 2-h CrCl and 24-h CrCl.
  
  
  RESULTS
  Mean GFR was 101 ± 18, 2-h CrCl 110 ± 20 and 24-h CrCl 106 ± 29 mL/min/1.73 m(2). Mean bias of 24 h CrCl was 7.4 [inter-quartile range -6.7 to 20.0] mL/min/1.73 m(2), precision (R(2)) 0.39 and 30% accuracy 82%. Mean FE(creat) was 110 ± 11%. FE(creat) correlated with body mass index (BMI) (r = 0.34, P < 0.001). Consequently, bias of 24-h CrCl increased from 2.7 (inter-quartile range -6.5 to 16.7) to 8.6 (inter-quartile range -5.8 to 20.5) and 12.6 (inter-quartile range 7.0 to 25.4) mL/min in subjects with BMI <25, 25-30 and >30 kg/m(2), respectively (P < 0.05). On multivariate analysis, BMI and gender were predictors of FE(creat).
  
  
  CONCLUSIONS
  CrCl systematically overestimates GFR in healthy subjects. The overestimation significantly correlates with BMI, with higher FE(creat) in subjects with higher BMI. The impact of BMI on tubular creatinine secretion can be accounted for, when using CrCl for GFR assessment in the normal to high range, by the following formula: GFR = 24-h CrCl - (22.75 + 0.76 × BMI - 0.29 × mean arterial pressure (-6.11 if female).
authors.affiliation: Division of Nephrology, Department of Internal Medicine, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: Steef J
authors.initials: SJ
authors.lastname: Sinkeler
authors.forename: Folkert W
authors.initials: FW
authors.lastname: Visser
authors.forename: Jan A
authors.initials: JA
authors.lastname: Krikken
authors.forename: Coen A
authors.initials: CA
authors.lastname: Stegeman
authors.forename: Jaap J
authors.initials: JJ
authors.lastname: Homan van der Heide
authors.forename: Gerjan
authors.initials: G
authors.lastname: Navis
mesh_terms: D015992:Body Mass Index; D002712:Chlorides / Q000378:metabolism; D017608:Chromium Compounds / Q000378:metabolism; D003404:Creatinine / Q000097:blood* / Q000652:urine*; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007674:Kidney Diseases / Q000517:prevention & control*; D007677:Kidney Function Tests; D016030:Kidney Transplantation; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D012016:Reference Values; D014019:Tissue Donors
chemical_list: D002712:Chlorides; D017608:Chromium Compounds; D003404:Creatinine; C017133:chromous chloride